The agency that controls Medicare and Medicaid payments is considering restricting its coverage of drug-coated cardiac stents because of safety concerns.

Drug-coated stents, which prop open clogged arteries and slowly release a chemical to keep them from closing up again, have recently come under fire because of fears that they increase the risk of blood clots over the bare-metal stents that they have largely replaced. Some studies suggest that the clotting is especially apparent when the coated variety is used "off label" in high-risk patients -- often diabetics and those who have had heart attacks -- even though the Food and Drug Administration hasn't approved the devices for use in these patients.

Now, the Centers for Medicare & Medicaid Services, or CMS, says it is considering reopening its decision about how broadly to cover the stents. An agency spokesman said such a process, known as a National Coverage Determination, could result in restricting coverage of the stents to FDA-approved uses, keeping coverage the same, or something in between.